This study is a laboratory companion to CALGB 9343: Evaluation of Lumpectomy. Tamoxifen and Irradiation of the Breast Compared with Lumpectomy plus Tamoxifen in Women Seventy Years of Age or Older Who have Estrogen Receptor Positive Carcinoma of the Breast that is less than 2 cm. and Clinically Negative Axillary Nodes: A Phase III Study. We hypothesize that a profile of molecular markers in the patients; primary tumors will be useful in predicting disease aggressiveness, clinical outcome, and potential response to radiation therapy. Using a portion of the paraffin block required for each patient in this study, we will test this hypothesis by performing the specific aims listed below. CALGB 9343 focuses on a cohort of women, 70 years of age or older, who are being treated for invasive breast cancer with lumpectomy and tamoxifen, with or without adjuvant radiation. The underlying hypothesis in this trial is that elderly women have a biologically less aggressive breast cancer than younger women and thus are amenable to less aggressive therapy (older women have greater frequency of well and moderately differentiated tumors, are more likely to be estrogen and progesterone receptor positive, and are more likely to have lower tumor proliferative rates. Eligibility for the clinical trial is clinically negative axillary nodes, however, since most or all of these patients will not receive axillary dissection, we will not have one of the most important staging parameters to predict a patient's risk of local and distant recurrence. Thus the identification of surrogate tumor markers to predict disease aggressiveness will be important. In addition, breast cancer in the elderly comprise 50 percent of newly diagnosed breast cancers in the United States yet, there is a scarcity of information on biologic characteristics of tumors in this age group and the use of these markers to predict outcome.